Housing
What size is your tank? 10 gal.
What temperature is your tank? 78*-80*
Does your tank have a filter? Yes.
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes.
What tank mates does your betta fish live with other fish? Yes 7 neon tetras

Food
What type of food do you feed your betta fish? Pellets - Hikari gold Betta pellets
How often do you feed your betta fish? Twice per day 3 pellets each time. One fasting day

Maintenance
How often do you perform a water change? Twice a week
What percentage of the water do you change when you perform a water change? 50%
What type of additives do you add to the water when you perform a water change? API Betta water conditioner

Water Parameters:
Have you tested your water? If so, what are the following parameters? So far Ph is 7.2 need to get ammonia test kit

Symptoms and Treatment
How has your betta fish's appearance changed? No
How has your betta fish's behavior changed? Very lethargic since I put him in 10 gal
When did you start noticing the symptoms? Yesterday
Have you started treating your fish? If so, how? No,
Does your fish have any history of being ill? No.
How old is your fish (approximately)? Maybe a few months? I got him at An LFS recently

Pataflafla is correct...it may be an adjustment period to not just the tank mates but to the tank size an filter/water movement as well....give him more time....If he doesn't adjust within a few days you may need to remove him and gradually increase the tank size in steps before you add him to the 10gal.......keep us posted....

I just got my first betta fish three days ago. Day before yesterday and yesterday morning, he was swimming around a lot, active and happy-looking. Then, I changed the water. It was starting to feel slimy, and I needed to put in the plastic thing with holes under the rocks to help keep the tank cleaner with the pump I have, so I needed to take out all of the water. I added all new water, put StressCoat in it, and waited till the heater heated it up, then added my fish back into it. So it was the same conditions as when I first introduced him to the tank on Saturday. When I got back to my room at 8 PM last night, he was kind of laying down under the heater (his favorite spot), and I thought he was sleeping, since he would move around a bit if I disturbed the tank. He moved a little this morning, but then settled back into his spot, still laying on the floor of the tank. I just got back from class and he was swimming around a bit, and it would pause and his head would start diving down and the rest would follow until he was lying on the bottom again. Now he's back under the heater, again laying on the bottom of the tank. What's wrong?
Also, he didn't eat last night or this morning, since he didn't move from his spot really. I keep him in a 1-gallon tank that has a heater and an air pump thing. The water temperature is 78. He's the only one in the tank.